A color developer containing an aromatic primary amine color developing agent has hitherto been utilized for the formation of photographic color images, and at present, it plays a major role in the image formation method in color photography. However, this color developer has a problem in that it is extremely easily oxidized with air or metals, and it is well known that the use of the oxidized developer for the formation of color images causes an increase of stain and fluctuation of sensitivity or gradation with the result that the desired photographic characteristic can not be obtained.
In view of the above situation, various means have heretofore been investigated so as to improve the preservability of color developers, and among them, a method of using both hydroxylamine and a sulfite ion has been most generally used. However, hydroxylamine yields ammonia, when decomposed, to cause fluctuation of gradation, while the hydroxylamine and sulfite ion reactively compete with the developing agent and thereby interfere with the coloring property of the developing agent. Accordingly, it is difficult to say that both of these compounds are preferred as a preservative for improving the preservability of the color developer.
Under the circumstances, various preservative have been investigated as substitutes for hydroxylamine and sulfite ions. For instance, there are mentioned the hydroxycarbonyl compounds described in U.S. Pat. No. 3,615,503 and British Patent No. 1,306,176, the .alpha.-aminocarbonyl compounds described in JP-A-52-143020 and JP-A-53-89425 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and the hydroxamic acids described in JP-A-52-27638, all of which, however, can not be said to be sufficient in the preservative capacity thereof, though they have little influence on the photographic characteristics in photographic processing. Especially in continuous processing in an automatic developing machine, if the amount of the photographic material to be processed is small or if the residence time of the replenisher to be applied to the machine is too long in the replenisher tank, the preservative compound would often have some harmful influence on the photographic characteristics in the photographic processing. Regarding the aromatic polyhydroxy compounds described in JP-A-56-47038 and U.S. Pat. Nos. 4,264,716 and 3,764,544, these are used in combination with hydroxylamine so as to inhibit decomposition of the hydroxylamine and to improve the stability of the processing liquid used. However, hydroxylamine has an influence on the coloring property of developing agents, as mentioned above, and is therefore unfavorable. In addition, the above-mentioned conventional hydroxylamine substitutes do not display a sufficient preservative capacity even when they are used in combination with aromatic polyhydroxy compounds.
As chelating agents, there are mentioned, for example, the aminopolycarboxylic acids described in JP-B-48-30496 and JP-B-44-30232, the organic phosphonic acids described in JP-A-56-97347, JP-B-56-39359 (the term "JP-B" as used herein means an "examined Japanese patent publication") and West German Patent 2,227639, the phosphonocarboxylic a ids described in JP-A-52-102726, JP-A-53-42730, JP-A-54-121127, JP-A-55-126241 and JP-A-55-65956 and the compounds described in JP-A-58-195845 and JP-A-58-203440 and JP-B-53-40900.
However, even though these compounds were used, sufficient preservative capacity still could not be attained, and these compounds were ineffective for stabilization of the photographic characteristics in continuous photographic processing.